The Applicant has developed a wide range of printers that employ pagewidth printheads instead of traditional reciprocating printhead designs. Pagewidth designs increase print speeds as the printhead does not traverse back and forth across the page to deposit a line of an image. The pagewidth printhead simply deposits the ink on the media as it moves past at high speeds. Such printheads have made it possible to perform full colour 1600 dpi printing at speeds in the vicinity of 60 pages per minute, speeds previously unattainable with conventional inkjet printers.
Printheads are typically controlled by a micro-processor within the printer, often referred to as a print engine controller (PEC). If a printhead is provided in a removable cartridge form, the PEC and the printhead must communicate via a detachable electrical interface—usually complementary contact pads. The contacts on the printhead should be close to the nozzles in the printhead integrated circuit (IC) for optimal electrical efficiency and operation. However, there are compelling reasons to keep the paper path adjacent the printhead straight instead of curved or angled. This requires the contacts to be positioned on a different side of the cartridge (not the side holding the printhead IC). The contacts then connect to the printhead IC via a flexible printhead circuit board (or flex PCB as it is known). The flex PCB wraps around a corner of the cartridge to connect the contacts to the printhead IC.
The conductive paths in the flex PCB are known as traces. As the flex PCB must bend around a corner, the traces can crack and break the connection. To combat this, the trace can be bifurcated prior to the bend and then reunited after the bend. If one branch of the bifurcated section cracks, the other branch maintains the connection. Unfortunately, splitting the trace into two and then joining it together again can give rise to electro-magnetic interference problems that create noise in the circuitry.
Making the traces wider is not an effective solution as wider traces are not significantly more crack resistant. Once the crack has initiated in the trace, it will propagate across the entire width relatively quickly and easily. Careful control of the bend radius is more effective at minimizing trace cracking, as is minimizing the number of traces that cross the bend in the flex PCB.
Pagewidth printheads present additional complications because of the large array of nozzles that must fire in a relatively short time. Firing many nozzles at once places a large current load on the system. This can generate high levels of inductance through the circuits which can cause voltage dips that are detrimental to operation. To avoid this, the flex PCB has a series of capacitors that discharge during a nozzle firing sequence to relieve the current load on the rest of the circuitry. Unfortunately, the capacitors and other components associated with the drive circuitry create additional traces that risk cracking in the bent section of the flex PCB.